1. Field of the Invention
The invention relates generally to a field-emitter-array and, more particularly, to a layered thin film-edged field-emitter-array and a method for its production using microelectronics fabrication and processing techniques.
2. Prior Art
Field-emitter-array electron sources and devices have been described essentially as being vertical devices in that the electrons are emitted from structures, such as points, wedges, "razor blades", in which the emission symmetry direction is normal, i.e., perpendicular, to the plane of the extraction grid or gate. These cold electron sources and devices can be made by a variety of known methods. All the known devices and fabrication methods rely on critical horizontal dimensional tolerances, and frequently on critical non-standard vacuum evaporation techniques or on difficult chemical etching procedures which are orientation-dependent. Often, they rely on micron and submicron lithography, usually electron beam lithography, to control the radius of curvature of each vertical emitter and/or to form the pointed or wedge structures. High resolution lithography is also required to form apertures in the extraction electrodes for the extraction of the electrons.
The techniques also usually depend on using single-crystal materials, e.g., silicon. Making large-size devices using these techniques is, at best, very difficult.
Furthermore, the known techniques require careful alignment or centering of the extraction aperture over the field emitter point or wedge, even though some of the reported processes use some sort of self-alignment procedure. Precision lithography is needed to correctly position the aperture holes relative to the emitters.
Another problem arises in the operation of prior-art devices: how can the current flow from the field emitter array be controlled without the extraction electrodes intercepting the current?
The following U.S. patents illustrate some of the foregoing problems and shortcomings of the prior art: Spindt et al. (U.S. Pat. No. 3,755,704), Gray et al. (U.S. Pat. No. 4,307,507), Christensen (U.S. Pat. No. 4,498,952) and Lee et al. (U.S. Pat. No. 4,827,177).
Spindt et al. discloses a technique for forming sharp-point emitters using metal and insulator films on a silicon substrate. An array of holes is formed through the upper metal and insulator films. Electrode material is deposited into each hole, normal to the surface. An evaporated aperture closure material is deposited on the same surface, at a shallow grazing angle from all sides of each hole, either with multiple distributed sources of the closure material, or using a single source and rotating the substrate. The size of each hole is gradually reduced, to limit the amount of electrode material passing through the aperture. In this way, emitters of a conical shape are formed.
While Spindt et al. starts with a thin-film laminate to form a field-emitter-array, and discloses one approach to the problem of alignment of the emitter with the aperture in the control electrode gate, the emitters are still disposed perpendicularly relative to the control electrode and the flow of electrons is normal to the control electrode or extraction grid.
Christensen describes a semiconductor-type process for fabricating a field-emitter-array from vertically-stacked thin films of alternating conductive and insulating layers. The resulting "optics" formed by the conductive layers modulate, deflect and focus the electron beams. These layers are aligned on a common axis above conical vertical emitters. As in Spindt et al., the electron flow from each emitter is normal to the control electrodes.
Lee et al. describes a single, co-planar thin-film field-emitter structure in which the emitter, control and anode electrodes are formed in the same plane from a single metallic layer. The electrodes are not formed from alternate vertically stacked metallic layers, as in the above patents. High gate interception of electrons results from this design.
Gray et al. discloses a method of making a field-emitter structure in which a mold of the desired configuration is formed by the orientation-dependent-etching of a single-crystal substrate through a perforated mask. The substrate is next coated with a material capable of emitting electrons under the influence of an electric field, and the substrate forming the mold is then partially or completely removed by etching to expose a plurality of sharp field emitter tips. The resulting field emitter structures can be made in flexible sheets which can be formed into appropriately-shaped cathodes for any desired electron gun design. As in the above patents, the emitters are disposed perpendicularly, and the electron flow is normal to the control electrodes.
Thus, while thin-film and microelectronics fabrication and processing techniques have been used in making field-emitter arrays, the resulting devices are still essentially vertical devices with the electron flow being normal to the plane of the extraction electrode, or they are single-film co-planar devices.